System comprising magnetically actuated motion control device

ABSTRACT

A system that includes a magnetically actuated motion control device comprising a housing defining a cavity and including a slot therethrough. A movable member is located within the cavity and is movable relative to the housing. A magnetic field generator located on either the housing or the movable member causes the housing to press against the movable member to develop a friction force.

FIELD OF THE INVENTION

[0001] This application is a divisional of pending U.S. patentapplication Ser. No. 09/537,365, filed Mar. 29, 2000.

[0002] The present invention relates to magnetically actuated motioncontrol device. In particular the present invention relates tomagnetically actuated motion control devices that vary contact pressurebetween a first member and a second member in accordance with agenerated magnetic field.

BACKGROUND AND RELATED ART

[0003] Magnetically actuated motion control devices such as magneticallycontrolled dampers or struts provide motion control, e.g., damping thatis controlled by the magnitude of an applied magnetic field. Much of thework in the area of magnetically controlled dampers has focused oneither electrorheological (ER) or magnetorheological (MR) dampers. Theprinciple underlying both of these types of damping devices is thatparticular fluids change viscosity in proportion to an applied electricor magnetic field. Thus, the damping force achievable with the fluid canbe controlled by controlling the applied field. Examples of ER and MRdampers are discussed in U.S. Pat. Nos. 5,018,606 and 5,384,330,respectively.

[0004] MR fluids have high yield strengths and viscosities, andtherefore are capable of generating greater damping forces than ERfluids. In addition, MR fluids are activated by easily produced magneticfields with simple low voltage electromagnetic coils. As a result,dampers employing MR fluids have become preferred over ER dampers.

[0005] Because ER and MR fluid dampers still involve fluid damping, thedampers must be manufactured with precise valving and seals. Inparticular, such dampers typically require a dynamic seal and acompliant containment member which are not particularly easy tomanufacture and assemble. Further, the fluid type dampers can havesignificant “off-state” forces which can further complicate manufactureand assembly. Off-state forces refer to those forces at work in thedamper when the damper is not energized.

[0006] The foregoing illustrates limitations known to exist in presentdevices and methods. Thus, it is apparent that it would be advantageousto provide an alternative directed to overcoming one or more of thelimitations set forth above. Accordingly, a suitable alternative isprovided including features more fully disclosed hereinafter.

SUMMARY OF THE DISCLOSURE

[0007] According to one aspect of the invention, a magnetically actuatedmotion control device is provided. The magnetically actuated motioncontrol device includes a housing, and movable member and a magneticfield generator located on either the housing or the movable member. Thehousing defines a cavity in which the movable member is located andincludes at least one slot. A magnetic field applied by the fieldgenerator causes the housing to press against the movable member andthereby provide friction damping.

[0008] According to another aspect of the invention, a sensor forsensing the position of a movable member relative to a housing of amagnetically controlled damper is provided. The sensor includes a firstmember secured to the housing, a second member, such as a slide, that iscoupled to the movable member so that the relative position of the firstmember and the second member relates the position of the movable memberwithin the housing. According to an exemplary embodiment, the movablemember can include a depression for receiving an extension on the secondmember of the sensor. The extension of the second member fits through aslot in the housing and into the depression to couple the second memberof the sensor to the movable member. In another embodiment, the secondportion of the sensor can be configured so as to be in rolling contactwith the movable member. In this embodiment, relative rotation betweenthe first member and the second member indicates relative motion betweenthe movable member and the housing.

[0009] The foregoing and other aspects will become apparent from thefollowing detailed description of the invention when considered inconjunction with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The objects and advantages of the invention will be understood byreading the following detailed description in conjunction with thedrawings in which:

[0011]FIG. 1 is a cutaway side sectional view of a first exemplaryembodiment of the present invention.

[0012]FIG. 2 is an end sectional view taken along section 2-2 in FIG. 1.

[0013]FIG. 3A is a side view of a housing according to a secondexemplary embodiment of the present invention.

[0014]FIG. 3B is an end sectional view taken along section 3-3 in FIG.3A.

[0015]FIG. 4A is a side view of a housing according to a third exemplaryembodiment of the present invention.

[0016]FIG. 4B is an end sectional view taken along section 4-4 in FIG.4A.

[0017]FIG. 5A is a side view of a housing according to a fourthexemplary embodiment of the present invention.

[0018]FIG. 5B is an end sectional view taken along section 5-5 in FIG.5A.

[0019]FIG. 6 is a cutaway side sectional view of a fifth exemplaryembodiment of the present invention.

[0020]FIG. 7 is a cutaway sectional view of a sixth exemplary embodimentaccording to the present invention.

[0021]FIG. 8 is a cutaway side sectional view of a seventh exemplaryembodiment according to the present invention.

[0022]FIG. 9 is a side cutaway sectional view of a eighth exemplaryembodiment of the present invention.

[0023]FIG. 10A is a schematic diagram illustrating the magnetic fieldproduced by permanent magnets in a damper according to the eighthexemplary embodiment.

[0024]FIG. 10B is a schematic diagram of the magnetic field produced bycoils in a damper according to the eighth exemplary embodiment.

[0025]FIG. 10C is a schematic diagram of the magnetic field resultingfrom the addition of the magnetic fields shown in FIGS. 10A and 10B.

[0026]FIG. 11 is a cutaway side sectional view of a ninth exemplaryembodiment of the present invention.

[0027]FIG. 12 is a graph showing the relationship between damping forceand current for a damper constructed in accordance with the presentinvention.

[0028]FIG. 13 is a perspective view of a tenth exemplary embodiment ofthe present invention.

[0029]FIG. 14 is a perspective exploded view of the embodiment shown inFIG. 13.

[0030]FIG. 15 is a side view of an embodiment of the present inventionincluding an outer layer of acoustically insulating material.

[0031]FIG. 16 is a cutaway side sectional view of an eleventh embodimentof the present invention.

[0032]FIG. 17 is an end sectional view taken along section 17-17 in FIG.16.

[0033]FIG. 18 is an exploded perspective view of the embodiment shown inFIGS. 16 and 17.

[0034]FIG. 19 is a cutaway side sectional view of a twelfth exemplaryembodiment according to the present invention.

[0035]FIG. 20 is a cutaway side sectional view of a thirteenth exemplaryembodiment according to the present invention.

[0036]FIG. 21 is a cutaway side sectional view of a fourteenth exemplaryembodiment according to the present invention.

[0037]FIG. 22 is a cutaway side sectional view of a fifteenth exemplaryembodiment according to the present invention.

[0038]FIG. 23 is an end sectional view taken along section 23-23 in FIG.22.

[0039]FIG. 24 is a schematic illustration of a washing machine employingan embodiment of the present invention.

[0040]FIG. 25 is a schematic illustration of an embodiment of thepresent invention used in an automobile, truck, or other vehicle.

[0041]FIG. 26A is a schematic illustration of an embodiment of thepresent invention used as a damper in a chair.

[0042]FIG. 26B is a schematic illustration of an embodiment of thepresent invention being used to control the tilt of the chair shown inFIG. 26A.

[0043]FIG. 27 is a schematic illustration of a height adjustable tableemploying an embodiment of the present invention.

[0044]FIG. 28A is a schematic illustration of an embodiment of thepresent invention used for locking a tilting door.

[0045]FIG. 28B is a schematic illustration of an embodiment the presentinvention used for locking a tilting work surface.

[0046]FIG. 29 is a side schematic illustration of an embodiment of thepresent invention used as a rotary brake in a force feedback steeringwheel.

[0047]FIG. 30 is a schematic side sectional illustration of a computerpointing device employing an embodiment of the present invention asrotary brakes.

[0048]FIG. 31 is a schematic side sectional illustration of an activeforce feedback steering wheel employing an embodiment of the presentinvention as a brake.

[0049]FIG. 32 is a schematic illustration of a device for holdingirregular objects employing an embodiment of the present invention.

[0050]FIG. 33 is a cutaway side sectional view of a sixteenth exemplaryembodiment according to the present invention.

[0051]FIG. 34 is a cutaway side sectional view of a seventeenthexemplary embodiment according to the present invention.

[0052]FIG. 35 is a cutaway side sectional view of a eighteenth exemplaryembodiment according to the present invention.

[0053]FIG. 36A is a schematic side sectional view of a nineteenthexemplary embodiment according to the present invention.

[0054]FIG. 36B is a sectional view taken along section 36-36 in FIG.36A.

[0055]FIG. 37A is a side view of the housing according to the embodimentshown in FIG. 36A.

[0056]FIG. 37B is an end view of the housing shown in FIG. 37A.

[0057]FIG. 38A is a side view of a housing according to a twentiethexemplary embodiment according to the present invention.

[0058]FIG. 38B is an end view of the housing shown in FIG. 38A.

[0059]FIG. 39 is a side sectional view of a twenty-first exemplaryembodiment of the present invention.

[0060]FIG. 39A is a partial view of the housing of FIG. 39.

[0061]FIG. 40 is a side sectional view of the embodiment shown in FIG.39 in an on-state.

[0062]FIG. 40A is a partial view of the housing of FIG. 40.

[0063]FIG. 41A is a sectional view taken along section 41-41 in FIG. 40.

[0064]FIG. 41B is a perspective view of a spring in the embodiment shownin FIG. 41A.

[0065]FIG. 41C is a perspective view of a bearing in the embodimentshown in FIG. 41A.

[0066]FIG. 42 is a cutaway side sectional view of a twenty-secondexemplary embodiment according to the present invention.

[0067]FIG. 43 is a cutaway side sectional view of a twenty-thirdembodiment according to the present invention.

[0068]FIG. 44 is a schematic view of the embodiment shown in FIG. 39employed in a car door.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0069] For a better understanding of the invention, the followingdetailed description refers to the accompanying drawings, whereinexemplary embodiments of the present invention are illustrated anddescribed.

[0070] The present invention relates to a magnetically actuatedalternative to traditional MR fluid motion control devices. Amagnetically actuated motion control device according to the presentinvention can be embodied as linear or rotary dampers, brakes, lockablestruts or position holding devices. The invention contains no MR fluid,yet provides a variable level of coulombic or friction damping that iscontrolled by the magnitude of the applied magnetic field.

[0071] In contrast to MR or ER fluid devices, a magnetically actuatedmotion control device according to the present invention is simple tomanufacture and relatively low cost. A magnetically actuated motioncontrol device according to the present invention also allows for veryloose mechanical tolerances and fit between components. In addition, amagnetically actuated motion control device according to the presentinvention does not require a dynamic seal or a compliant containmentmember as does a fluid type damper, and is therefore relatively easy tomanufacture and assemble. Further, a magnetically actuated motioncontrol device according to the present invention has particularly lowoff-state forces which provide for a wide dynamic range between theoff-state and a maximum damping force.

[0072] An example of a magnetically actuated motion control deviceaccording to the present invention includes a magnetically permeabletubular housing that moves relative to an electromagnetic piston andincludes one or more coils, an associated magnetically permeable core orcore pieces and associated pole regions. Although the housing in thisexample is tubular, a housing can be of any suitable cross section,including, but not limited to a rectangular cross section. The poleregions are located near an interface between the piston and the housingand carry magnetic flux in a generally radial direction with respect toa longitudinal axis running along the housing. The housing includes atleast one slot but typically includes an array of slots. The housingslots allow the housing to flex and constrict radially when a magneticfield is applied by directing current through the coils. In so doing,the inner surface of the housing squeezes against the outer surface ofthe piston with a normal force that is approximately proportional to themagnitude of the applied magnetic field. Thus, the housing acts like amagnetically actuated collet that squeezes the piston to resist relativemovement between the housing and the piston. Generally, the magnitude ofthe applied magnetic field is proportional to the electric currentsupplied to the coil. The damping force thus depends on the coefficientof friction between the inner surface of the housing and the outersurface of the piston and the normal force between these surfaces, whichis dependent on the magnetic field produced by running current throughthe coils.

[0073] The invention allows for the accommodation of very loosemechanical tolerances or fit between the housing and the piston. Becausethe present invention does not require a dynamic seal or compliantcontainment member, it offers particularly low off-state forces and issimple to manufacture and assemble.

[0074] The present invention is particularly suitable for makinglow-cost, high-volume linear dampers for use in household appliancessuch as washing machines. Other applications for magnetically actuatedmotion control devices according to the present invention include simplerotary or linear brakes for controlling mechanical motions inside officeequipment such as copiers or printers, e.g., paper feed mechanisms.Additional applications for magnetically actuated motion control devicesaccording to the present invention include dampers for use assemi-active control elements in conjunction with ultra-low vibrationtables and platforms. Magnetically actuated motion control devicesaccording to the present invention can also be used as latching orlocking mechanisms in office furniture, e.g., props and latches fordoors, drawers, etc. Still other applications include exerciseequipment, rehabilitation equipment, joysticks, seismic structuralcontrol dampers, avionics semi-active control devices, machine toolfixturing devices, ventilation system flaps and doors in automobiles,and sliding doors in vehicles, etc.

[0075] Magnetically actuated motion control devices according to thepresent invention can also be used in the area of haptics. The field ofhaptics includes devices used in computer peripherals such asforce-feedback steering wheels, programable detents, computer pointingdevices and joysticks used with games and other software. This fieldalso includes industrial force feedback mechanisms such as steeringwheels on steer-by-wire vehicles.

[0076] Yet another application is to use either linear or rotaryembodiments of the invention in conjunction with pneumatic and hydraulicactuators to enable precision position and velocity control.

[0077] Turning to the drawings, a first exemplary embodiment of amagnetically actuated motion control device according to the presentinvention is shown in FIGS. 1 and 2. The first embodiment motion controldevice is a damper 101 and includes a housing 103 defining a cavity 105in which a piston 107 is located. The housing 103 includes a least onelongitudinal slot 109 (five of eight such slots can be seen in FIG. 1).The housing shown in FIG. 1 includes a plurality of slots that passthrough the housing wall to define flexible bands, tabs, or fingers 111.The slots 109 extend through the wall of the housing 103 and extendnearly the entire length of the housing 103. Although narrow slots areillustrated in the Figures, it should be understood that a suitable wideslot could also be provided in the housing.

[0078] The piston 107 includes a shaft 112 having a magnetically activeportion 113 made up of at least one, and preferably two electromagneticcoils 115 set in a magnetically permeable core 117. Although here themagnetically permeable core 117 is hollow, the core can alternatively bea solid bobbin. A hollow core allows space for connecting wires or foran axial screw or rivet. However, a solid core is preferable becausemagnetic saturation of the core is reduced.

[0079] In addition, the core can be made up of a plurality of corepieces. A current source 118 supplies current to the coils 115 throughwires 119. Each end of the damper preferably includes a structure whichfacilitates attaching damper 101 to other structures, such as clevis eye121 for attaching the end to a portion of a damped component.

[0080] Current flowing through the coils 115 creates a magnetic fieldthat draws the housing 103 in toward the piston 107. For this purpose,the housing 103 is formed of a material which will be attracted by themagnetic field. Examples include, but are not limited to, steels andother iron alloys. The amount of current flowing through the coils 115is generally directly proportional to the magnitude of the magneticfield generated. Thus, control of the electric current flowing throughthe coils 115 can be used to control the normal or pressing forcebetween the inner surface of the housing 103 and the outer surface ofthe piston 107, thereby controlling the damping effect of the damper101.

[0081] An illustration of the damping effect can be seen in the endsectional view shown in FIG. 2, which shows the relationship of theslotted housing 103 with respect to the piston 107. When no magneticfield is applied, the piston 107, and particularly the active portion113, fits loosely within the housing 103 to define a small radialclearance 123 between the housing 103 and the magnetically activeportion 113 of the piston 107. That is, the housing 103 is relaxed anddoes not press against the piston 107. When current is supplied to thecoils 115 the magnetic field generated causes the flexible fingers 111in the housing 103 to be attracted radially inward as indicated by thearrows 125 such that the housing 103 squeezes the piston 107 with aforce proportional to the applied magnetic field, and therefore theapplied current.

[0082] The slotted housing 103 and the core 117 of the piston 107 arepreferably made from low carbon, high permeability steel, although othermagnetically permeable materials can be used. The slots 109 arepreferably evenly spaced around the circumference of the housing 103 sothat axial-periodic symmetry is maintained. The pair of coils 115 ispreferably wired such that they produce magnetic fields in oppositedirections. This configuration allows the magnetic field produced byeach coil 115 to add rather than cancel in an area between the coils115.

[0083] The configuration of the slots in the housing of the damper canbe varied to tune the flexibility of a housing. FIGS. 3A and 3Billustrate a housing 127 that includes fewer longitudinal slots 109, andtherefore has less flexibility than a comparable housing having a largernumber of slots. Longitudinal slots 109 may also be carried through toan open end 129 of a housing 131 as shown in FIGS. 4A and 4B. Slots 109carried through to the end 129 create a flexible housing 131 whichpromotes full contact between the housing 131 and the piston when themagnetic field is applied. Such a slot configuration may be particularlyuseful when the housing 131 is made from a thick-wall tubing. Greaterhousing flexibility can also be obtained by connecting pairs of slots109 in a housing 133 with a cross-slot 135 to form flexible fingers 137having free ends 138 as shown in FIGS. 5A and 5B.

[0084] Depending on the thickness of the housing material and itsconsequent ability to carry magnetic flux (permeability), and also onthe magnitude of the desired damping force, the number of coils 115 canvary from the embodiment shown in FIGS. 1 and 2. For example, asingle-coil embodiment 139 is shown in FIG. 6 and a 4-coil embodiment141 is shown in FIG. 7. Except for the number of coils 115, and a solidcore 143 rather than the hollow core described above, the embodimentsshown in FIGS. 6 and 7 are identical to the embodiment shown in FIGS. 1and 2. More coils 115 are preferable when the thickness of the housingis small in order to avoid magnetic saturation of the housing. Magneticsaturation refers to the maximum amount of magnetization a material canattain, as will be readily appreciated by one of ordinary skill in theart. The thickness of the housing limits the amount of magnetizationthat can be induced in the portion of the housing adjacent to the coils.

[0085] In some applications of the invention it is desirable to have themagnetic field, and therefore the damping force, applied most of thetime with only short instances of turning the damping off. This can beaccomplished by adding one or more permanent magnets to the system. Apermanent magnet can be used in the damper so that the damper is in itson-state and the housing pressing against the piston when no current isapplied to the electromagnetic coil. The electro-magnetic coil serves tocancel the field of the permanent magnet as current is applied toprogressively turn the damper off.

[0086] A seventh exemplary embodiment of the motion control device ofthe present invention is illustrated in FIG. 8. As seen in FIG. 8, twoaxially polarized (i.e., the opposite faces of the disks are theopposite poles of the magnets) disk magnets 143 are positioned andoriented to bias a damper 145 into an on-state, i.e., a condition inwhich the housing is magnetically attracted to the piston. Amagnetically active portion 147 of a piston 149 includes three corepieces 151 between which the disk magnets 143 are located. The diskmagnets 143 are located immediately radially inward of the coils 115.The disk magnets 143 pull the housing 103 and the piston 149 together.In order to turn the damping off, the magnetic fields produced by thepermanent disk magnets 143 are at least in part, and preferablycompletely canceled by applying current to the pair of coils 115, whicheach generate magnetic fields that oppose those of the permanent magnets143.

[0087] An eighth exemplary embodiment of the motion control device ofthe present invention is illustrated in FIG. 9. In this case theelectromagnets do not cancel the magnetic field in all directions.Rather, the electromagnets cause the field of the permanent magnet to beredirected to a different path.

[0088] Like the embodiment shown in FIG. 8, the embodiment of a damper150 according to the present invention shown in FIG. 9 includes thehousing 103 having the same structure as that shown in FIGS. 1 and 2.According to the embodiment shown in FIG. 9, a magnetically activeportion 152 of a piston 153 includes axially-polarized permanent ringmagnets 155 located immediately radially inward of the coils 115. Thecoils and ring magnets are located between magnetically permeable corepieces 157 so as to define non-magnetic gaps 159 in the center of eachring magnet 155. Gaps 159 are less magnetically permeable than corepieces 157, and therefore cause less magnetic flux through the center ofthe magnetically active portion 152. The core pieces 157 and ringmagnets 155 are held together by a non-magnetic connector 161. Theconnector 161 is non-magnetic to prevent the generated magnetic fieldfrom being shunted away from the interface between the housing 103 andthe magnetically active portion 152. Alternatively, the core pieces 157can be held together by an adhesive. Any suitable adhesive can be used,including but not limited to epoxys and cyanoacrylates.

[0089] As is schematically shown in FIG. 10A, the non-magnetic gaps 159at the center of the ring magnets 155 allow very little magnetic flux tofollow flanking paths through the non-magnetic gaps 159 at the center ofthe ring magnets 155. As a result, a magnetic field 162 through thehousing 103 has a much lower reluctance (resistance to carrying amagnetic field) than the flux path through the center of each of thering magnets 155 and therefore radially draws the housing 103 and thepiston 149 together, as described above. In order to reduce the dampingforce, current is applied to the electromagnetic coils 115 which producea magnetic field 163, as schematically shown in FIG. 10B. The currentcan be adjusted such that the magnitude of the field produced by thecoils is equal to, but opposite, that of the ring magnets 155 where thefield paths cross into the housing 103. The magnetic field 163 adds tothat produced by the ring magnets 155 to yield a net magnetic field 165shown in FIG. 10C. That is, the magnetic field of each of the permanentring magnets 155 is redirected to flow through the high reluctance paththrough the open center of the ring magnets 155. The magnetic field atthe interface between the housing 103 and the piston that produces theattraction between the housing 103 and the piston 149 is canceled, andhence the damping force of the damper is reduced or entirely canceled.

[0090] A ninth exemplary embodiment of the motion control device of thepresent invention is illustrated in FIG. 11. As shown in FIG. 11, aspring 167 can be added to an end of a damper according to the presentinvention to form a strut 169. The damper shown in FIG. 11 is identicalin structure to that shown in FIGS. 1 and 2, except that the spring 167is provided between the end 171 of the piston 107 and closed end 173 ofthe housing 103. In a mechanical system the strut 169 provides thedesired spring stiffness in addition to a controllable level of dampingforce. In addition, as schematically shown in FIG. 11, a mechanical stop175 is added to the end of the housing 103 to hold the piston 107 in thehousing 103 and allow the spring 167 to be preloaded. The mechanicalstop 175 can optionally be included with damper embodiments as well.

[0091] Measured performance of a damper constructed according to thepresent invention is shown in the graph comprising FIG. 12. For purposesof plotting the performance graph, the damper housing was constructedfrom low-carbon steel tubing having a 1.125 inch (28.58 mm) outerdiameter and 1.000 inch (25.40 mm) inner diameter. The steel part of thehousing was 5.0 inches (127 mm) long. Four lengthwise slits eachapproximately 0.040 inches (1 mm) wide 4.25 inches (108 mm) long wereformed in the housing. The piston included two coils wound onto a lowcarbon steel double bobbin having an overall length of 1.0 inches (25.4mm). The diameter of the steel poles of the piston was 0.990 inches(25.15 mm). The axial length of the two outer pole sections were each0.145 inches (3.68 mm). The center pole section was 0.290 inches (7.37mm) long. The diameter of the solid center core of the piston was 0.689inches (17.5 mm). The two coils were each wound with 350 turns of 35 AWGmagnet wire and were connected in series. The total resistance of thetwo coils was approximately 48 ohms. The total usable stroke of thedamper was about 3 inches (76 mm).

[0092] Turning now to the graph, initially, at low current, the exampledamper displays a proportionate, nearly linear behavior which then rollsoff as magnetic saturation effects begin to dominate as can be seen inFIG. 12. The damping force that is produced is almost perfectlycoulombic with little or no velocity dependence. That is, the dampingforce is almost directly dependent on the current supplied to the coils.The data shown are peak forces obtained with the damper undergoingsinusoidal excitation with a ±0.5 inches (12.7 mm) amplitude and a peakspeed of 4 inches/sec (102 mm/s). A curve obtained with a peak speed of1 inch/sec (25.4 mm/sec) appeared to be nearly identical.

[0093] Although axial motion of the piston relative to the housing iswhat has been discussed thus far, a damper according to the presentinvention will also function as a rotary damper with the piston rotatingrelative to the housing.

[0094] A tenth exemplary embodiment of the motion control device of thepresent invention is illustrated in FIGS. 13 and 14. FIG. 13 shows anassembled example of a rotational embodiment according to the presentinvention, with portions broken away to show some interior elements.FIG. 14 shows the embodiment shown in FIG. 13 partially disassembled. Inthis embodiment a coil 177 wound around a center steel bobbin 179 form astator 181. The stator 181 is positioned within a cavity defined by, andfor rotation relative to, a slotted housing 183. Slots 185 are connectedby cross-slots 186 to define fingers 187, which impart a high degree offlexibility to the housing 183. The highly flexible housing 183 allowsmaximum contact between the stator 181 and the housing 183 when themagnetic field is energized. Bearings 188 are included in the stator 181to support a shaft 190 with which the housing 183 rotates.

[0095] A damper according to the present invention generates strongcoulombic pressing forces when the outer surface of the magneticallyactive portion of the piston or stator makes direct contact with theinner surface of the steel housing. In fact, the inventor herein hasfound that damper performance actually improves after being initiallyoperated due to an apparent “wearing-in” process. During the wearing-inprocess friction between the surfaces of the housing and the pistoncauses some wear to occur which effectively laps or burnishes thecontacting surfaces such that “high spots” (large surface features) areremoved and the housing and piston (or stator) contact more intimately.This improves the efficiency of the magnetic circuit and increases totalcontact surface area so that the overall damping force is increased.

[0096] In some applications of the present invention, it is desirable toplace a layer of damping material or acoustic foam 189 around theoutside of the housing as seen on the exemplary damper shown in FIG. 15.The components of the damper shown in FIG. 15 are identical to theexemplary dampers discussed with respect to FIGS. 1-14. Such anacoustically insulating material will serve to attenuate any highfrequency squeaking, rubbing or clanking sounds that may occur due to ametal housing moving against a metal piston. The desirability of suchadded acoustic material depends on a number of factors, including: theactual thickness of the housing; the resonant characteristics of thehousing; the looseness of the fit between the housing and the piston,the alignment of the parts during application of the damper; and thepresence of elastomeric bushings in the clevis eyes used to mount thedamper. Lubricant (grease or oil) can also be added so that the parts ofthe damper slide smoothly relative to each other in the off-state.Suitable acoustic material will be readily apparent to one of ordinaryskill in the art.

[0097] A similar quieting effect can be achieved by adding anintermediary friction increasing layer to the rubbing surfaces of thepiston or stator, or the inner surfaces of the housing. Examples of suchmaterials may be a thin polymeric layer such as polyethylene or nylon,or a composite friction material such as that typically used in vehicleclutches and brakes. Such a friction layer eliminates metal to metalcontact and reduces long term wear. However, the presence of such layerof friction material will in general make the magnetic circuit lessefficient. Unless the friction material has a high permeability like lowcarbon steel it increases the reluctance of the magnetic circuitdramatically and lowers the amount of damping force when the damper isin the on-state.

[0098] According to yet another embodiment of the present invention, amagnetically controlled damper can further include an integratedposition sensor. Exemplary embodiments of a damper including a positionsensor according to the present invention are shown in FIGS. 16-23.Preferably, a magnetic friction damper 191 includes sensor 193, such asa linear potentiometer, including a first portion 194 and a slider 196.The first portion is attached to the housing 103 by brackets 198. Theslider 196 is coupled to the damper piston 195 by a small engagement pin197 that passes through one of a plurality of slots 109 in the housing103 of the magnetic friction damper 191.

[0099] A eleventh exemplary embodiment of the motion control device ofthe present invention is illustrated in FIGS. 16-18. FIGS. 16-18 show adamper similar to the damper shown in FIGS. 1 and 2. Otherwise identicalto the piston shown in FIGS. 1 and 2, the piston 195 includes acircumferential groove 199 between electromagnetic coils 115. The sensor193 is mounted along the side of the damper housing with brackets 198such that an extension, such as the pin 197 of the slider 196 on thepotentiometer 193, can pass through one of the longitudinal slots 109 inthe damper housing 103. The groove 199 in the damper piston 195 acceptsthe pin 197 and causes the slider 196 to move longitudinally in concertwith the piston 195 while permitting relative rotational movementbetween the piston and the housing. Thus, for example, electricalresistance of a potentiometer varies in proportion to the pistondisplacement in the housing, thereby indicating the relative position ofthe housing 103 and the piston 195.

[0100] Alternatively or in addition to measuring linear displacementwith the sensor 193, the sensor can be used to measure the relativevelocity or acceleration of the housing 103 and the piston 195.Furthermore, sensor 193 can be a velocity sensor or an accelerometer,which are readily commercially available and with which one of ordinaryskill in the art is well acquainted. A device for interpreting thesignal from sensor 193, such as a general purpose computer 200 having amemory 201, is in electrical communication with electrical connections202 on the sensor 193. Computer 200 can further be provided with logicin the memory 201 which can determine relative position, velocity, oracceleration based on the electrical signals sent by the sensor 193, andcan store data representative of one or more of these parameters.Because one of ordinary skill in the art readily appreciates the detailsof the use of such a computer 200 and logic usable with sensor 193,further details will not be provided herein.

[0101] A circumferential groove 199 rather than a hole in the piston 195is preferred because the circumferential groove 199 does not inhibitrotational motion of the piston 195. Allowing free rotational motion ofthe piston 195 relative to the housing 103 is important so that theclevis eyes 121 at the ends of the damper 191, when provided, can beeasily properly aligned with the mounting pins in the components towhich the damper 191 is attached so that the damper 191 does not bindduring use.

[0102] Twelfth, thirteenth and fourteenth exemplary embodiments of themotion control device are illustrated in FIGS. 19, 20 and 21respectively. As seen in FIGS. 19-21, a circumferential groove can belocated on other parts of the piston 195 as well. For example, as seenin the embodiment shown in FIG. 19, a groove 203 is formed into theshaft of the piston 195 just behind a magnetically active portion 205 ofthe piston. In the embodiment shown in FIG. 20, a groove 207 is formedbetween a lip 209 formed into the piston 195 and a rear end 211 of themagnetically active portion 205 of the piston 195. In the embodimentshown in FIG. 21, a disk-shaped member 213 is attached to a free end 215of the piston 195 to define a groove 217. Other than the arrangement ofthe circumferential groove the embodiments shown in FIGS. 19-21 areidentical to the embodiment shown in FIGS. 16-18.

[0103] An experimental example of a damper including a position sensorwas tested by the inventor herein. The prototype utilized a Panasonicpotentiometer (part number EVA-JQLR15B14, Matsushita Electric (PanasonicU.S.A.), New York, N.Y., U.S. distributers include DigiKey and NewarkElectronics) with a working stroke of 3.94 inches (100 mm). Electricalresistance varied linearly from 0 to 10 Kohms. The potentiometer wasmounted to the damper housing using hot-melt adhesive. The originalrectangular extension on the slider was modified into the form of asmall diameter pin to fit through one of the longitudinal slots in themagnetic friction damper housing. In the example, the groove in thepiston was made by adding a small, spaced plastic disk to the end of anexisting piston as shown in FIG. 21. The final result was an integratedvariable resistance sensor whose output varied linearly with theposition of the damper piston. Further, the pin and groove geometryallowed free rotational motion of the piston within the housing, afeature that allowed for proper alignment of the clevis eyes duringdamper installation and use.

[0104] A fifteenth exemplary embodiment of the motion control device ofthe present invention is illustrated in FIGS. 22 and 23. Anotherexemplary embodiment of a damper including a position sensor is shown ifFIGS. 22 and 23. In this embodiment a rotary sensor 219 (e.g., a rotarypotentiometer) is used in the position sensor. Alternatively, a rotaryoptical encoder can be used in the position sensor. The rotary sensor219 is mounted to the housing by a bracket 220 and is coupled to themotion of a piston 221 by means of the integrated rack and pinion system223. A pinion gear 225 is coupled to the rotary sensor 219 (or opticalencoder) by an axle 227. The piston 221 includes a shaft 228 that ismolded (of, e.g., plastic) or otherwise formed to include a rack 229. Itis preferable to allow relative rotation between the piston and thepinion gear. Therefore, it is preferable that the rack 229 is formedaround the entire circumference of the piston 221.

[0105] In addition to the variable resistance sensors discussed above,other sensing devices may alternatively be used, including variableinductance or variable capacitance sensors, optical encoders, flex orbend sensors etc. and are all within the spirit and scope of the presentinvention. As discussed in reference to FIGS. 16-23 a sensor can be usedto measure relative velocity or acceleration as well as relativeposition between a piston and a housing.

[0106] Further, although the magnetic damper including a position sensorhas been described in the context of collet type dampers, the sameposition sensors may be included with MR or ER dampers. Examples of suchMR or ER dampers are described in U.S. Pat. Nos. 5,284,330, 5,277,281and 5,018,606, which are herein incorporated by reference in theirentireties.

[0107] Magnetically actuated motion control devices according to thepresent invention, including those described herein, are useful in manyapplications. FIGS. 24-32 illustrate a number of exemplary applicationsfor the present invention device. For example, FIG. 24 shows the use ofmagnetically controllable dampers according to the present invention 230in a washing machine 231. Magnetically controllable friction dampers canprovide a high level of damping when the washing machine 231 passesduring a resonance cycle and can be turned off during high speed spin toprovide optimum isolation of the spinning basket or drum 232.

[0108]FIG. 25 shows several possible uses of the present invention in anautomobile, truck, or other vehicle. Magnetically actuated motioncontrol devices according to the present invention can be used as asemi-active seat suspension when located between a seat 233 and anassociated base 235. Dampers according to the present invention can alsobe used as a locking element 237 in a steering column 239 including tiltand telescope mechanisms 241, 243. A magnetically actuated motioncontrol device 230 in its on-state locks the steering column 239 inplace. In its off-state, the damper allows the steering wheel to tiltand telescope into a desired position. Other applications in motorvehicles include the use of a damper as an interlock mechanism ingearshift mechanisms (not illustrated).

[0109] Another application for the invention is as a locking member 245for various types of furniture such as office chairs, for example. FIG.26A illustrates the use of a magnetically actuated motion control device230 in a height adjustor 245 of an office chair 247. FIG. 26Billustrates the use of a magnetically actuated motion control device 230as a locking mechanism 249 for the back tilt motion of the chair 247 andas a locking mechanism 250 for a height adjustable armrest 252 of thechair 247, and which can be connected between the armrest 252 and eithera seat 254 or a backrest 256 of the chair 247. An electrical control 251is used by an operator to selectively turn off the magnetically actuatedmotion control device 230, thereby allowing the chair 247 to tilt.

[0110]FIG. 27 illustrates the use of magnetically actuated motioncontrol device 230 as a locking mechanism 253 for an adjustable heighttable 255. The adjustable height table 255 also includes a control 258wired to the locking mechanism 253. The control 258 selectively allowsselective locking of the adjustable table 255 by alternatively turningthe dampers on and off.

[0111]FIGS. 28A and 28B show a magnetically actuated motion controldevice 230 according to the present invention used as a lockingmechanism for a tilting work surface 257 into position (FIG. 28B) or forlocking a flipper door 259 into place (FIG. 28A).

[0112] Another area of application for the motion control device of thepresent invention is the area of haptics, where a linear or rotaryembodiment of the invention may be used to provide tactile forcefeedback to an operator. FIG. 29 illustrates a force-feedback steeringwheel 261 that uses a rotary damper 263, such as that described inreference to FIGS. 13 and 14. Such a device can also be used in“steer-by-wire” mechanisms on vehicles such as cars, trucks orindustrial jitneys and forklifts. The present invention can also be usedin computer games as a force-feedback steering wheel that is responsiveto virtual action in a game. In the example shown in FIG. 29, the damper263 is coupled to a rotary position sensor 265 so that the damping canbe coupled to the position of the steering wheel.

[0113] The present invention can also be used as a small controllablefriction brake inside computer pointing devices, such as a computermouse 267 as shown in FIG. 30. The mouse 267 includes a mouse ball 269that is in rolling contact with a y-drive pinion 271 and an x-drivepinion 273. The drive pinions 271, 273 are each respectively coupled toa y-encoder wheel 275 and a x-encoder wheel 277 with a rotary brake 279of the type described in reference to FIGS. 13 and 14, for example. Eachencoder wheel 275, 277 is positioned so as to rotate through an encodersensor 280. The rotation of an encoder wheel is sensed by a respectiveencoder which sends an electrical signal representing the movement ofthe mouse ball 273 in an x-y plane which passes through pinions 271,273.

[0114] The invention can also be used to provide an active forcefeedback steering wheel 281 as shown in FIG. 31. In this application apair of clutches 283, 285, similar in structure to the rotary damperdescribed with reference to FIGS. 13 and 14, are used to selectivelycouple the steering wheel 281 to either clockwise or counter-clockwiserotating housings 287, 289. In a clutch arrangement, the stator and thehousing are each rotatable, and are rotatable relative to one another. Amotor 291 is coupled to clockwise and counter-clockwise housings 287,289 by a pinion drive 293. A shaft 295 extending from the steering wheelpasses through the housing 289 and is coupled to stators 297, 299 of theclutches 283, 285, respectively. The shaft 295 can include bearings orother similar structures where the shaft passes through the housings287, 289, to permit relative rotational movement between the shaft andthe housings. A rotary position sensor 298 is coupled to the end ofshaft 295 to detect the rotation of the steering wheel 281. The stators297, 299, provide friction damping in the clockwise andcounter-clockwise directions as in the manner described with referenceto FIGS. 13 and 14 with contact surfaces 301, 303. Thus, the steeringwheel 281 can actually be forced to turn with a prescribed amount offorce in either direction with the ultimate driving source being asimple single direction motor 291.

[0115] The invention can also be used in flexible fixturing systems suchas the fixturing system 305, schematically illustrated in FIG. 32. Inthis example, an array of struts 307, like those described in referenceto FIG. 11, are each coupled to extensions 309 and are used to hold anirregularly shaped object 311 in position for machining or gauging ofthe object 311. Each of the struts 307 can selectively lock or releasean extension 309 so that objects of various sizes and shapes can beaccommodated and held in place.

[0116] In addition to the embodiments of the present invention shown inFIGS. 1-23 and described hereinabove, other embodiments of the presentinvention shown in FIGS. 33-43 can be interchanged for the exemplarymagnetically actuated control devices illustrated in the applicationsdescribed with reference to FIGS. 24-32.

[0117] The sixteenth preferred embodiment of the motion control deviceis illustrated in FIG. 33. As seen in FIG. 33, the motion control deviceis comprised of a damper 313 that includes a housing 103 having slots109 and a piston 315 having a magnetically active portion 317 thatincludes a permanent disk magnet 319 sandwiched between core pieces 321.The core pieces 321 are held together by the magnetic field generated bythe permanent magnet 319, eliminating the need for connectors oradhesives in the magnetically active portion of the piston 315. Thus,the assembly of the damper 313 is greatly simplified. Because themagnetic field generated by the permanent magnet 319 cannot be varied,the damper 313 is always in an on-state. That is, the housing 103 alwayssqueezes the piston 315 with the same force.

[0118] Seventeenth and eighteenth exemplary embodiments of the motioncontrol device of the present invention are illustrated in FIGS. 34 and35. However, as seen in FIGS. 34 and 35, the squeezing force between thehousing and the magnetically active portion of the piston can be variedby introducing a variable width gap into the magnetically active portionof the damper. As seen in FIG. 34, a damper 323 of this type includes ahousing 103 including a plurality of slots 109, within which a hollowpiston 325 is located. A magnetically active portion 326 of the piston325 includes an end 327 connected to a control rod 329. The end 327includes an axially polarized disk magnet 330 that is sandwiched betweena cap piece 332 and a first pole piece 331. The control rod 329 isattached to the cap piece 332.

[0119] According to an exemplary embodiment shown in FIG. 34, a secondpole piece 333 is attached to the hollow piston 325. A clearance 335between the control rod 329 and the second pole piece 333 allows thesecond pole piece 333 to slide relative to the control rod 329. A lever337 located on the outer surface of the piston 325 is connected to thecontrol rod 329 through an opening 338 in the piston 325 so that as thelever 337 is turned, the control rod 329 pushes the end 327 of themagnetically active portion 326 toward or away from the second polepiece 333 attached to the hollow piston 325. In this way, an air gap 339of variable size is introduced into the magnetically active portion 326.The gap 339 increases the reluctance within the magnetically activeportion 326, thereby diminishing both the force with which the housing103 squeezes the piston 325, and also the frictional damping forceproduced by the damper.

[0120] Alternatively, as seen in FIG. 35, a damper 341 according to thepresent invention can include a control rod 343 having a threaded end345 that threads into a tapped second pole piece 347 that is attached tothe hollow piston 325. Like the embodiment shown in FIG. 34, the controlrod 343 is attached (at the threaded end 345) to a cap piece 349 thatsandwiches an axially polarized disk magnet 350 with a first pole piece351. The control rod 343 is connected to a knob 353 that is exposedthrough an opening 355 in the hollow piston 325. Rotating the knob 353rotates the control rod 343 and causes the tapped second pole piece 347to move relative to the cap piece 349. In this way, a variable air gap357 is introduced into the magnetically active portion. As discussed inreference to the embodiment shown in FIG. 34, the variable gap 357 canbe used to control (diminish) the damping force produced by the damper.

[0121] Nineteenth and twentieth exemplary embodiments of the motioncontrol device of the present invention are illustrated by FIGS.36A-37B, and 38A-38B respectively. As seen in FIGS. 36A-38B, accordingto the present invention the components of a magnetically actuatedmotion control device can be reversed with respect to the otherexemplary embodiments discussed thus far. For example, as seen in FIGS.36A and 36B, a damper 359 includes a housing 361 that defines a cavity363 in which a piston 365 is located. The piston 365 includes four slots367 that extend from an open end 369 of the piston 365. Although thepiston 365 is tubular, a piston can have any suitable cross-sectionalarea such as square, cylindrical etc. A magnetic field generator, suchas coils 371 (shown schematically), is located in a magneticallypermeable assembly 373 having pole pieces 375. At least a portion of theslotted piston 365 is magnetically permeable so that when a magneticfield is generated by the coils 371, the piston flexes and pressesoutward against the pole pieces 375 of the magnetic assembly 371 locatedon the housing 361. Accordingly, the friction damping force can becontrolled by controlling the magnetic field generated by the coils 371.

[0122] As seen in FIGS. 37A and 37B, the piston 365 is hollow. A hollowpiston is preferred because a hollow piston can easily flex outward inresponse to an applied magnetic field. However, according to anembodiment shown in FIGS. 38A and 38B, a piston 377 can be solid. Slots379 extend through the solid piston 377 to define bands, sections, tabs,or fingers 381. The fingers 381 flex outward in response to an appliedmagnetic field to produce a frictional damping force. An advantage ofhaving a solid piston is that magnetic saturation of the piston can bemitigated.

[0123] Other embodiments of a magnetically actuated motion controldevice according to the present invention include bearing componentsthat contact the components of the magnetically controlled motioncontrol device, e.g., a housing and a piston, and provide smoothrelative motion between the components when the motion control device isin its off-state.

[0124] For example, a twenty-first exemplary embodiment of the motioncontrol device of the present invention is illustrated in FIGS. 21 and39-41C. A magnetically actuated motion control device 383 includes apiston 385 which fits within a housing 387. The piston 385 includes oneor more longitudinal slots 388 which extend through an end 389 of thepiston 385 to define one or more fingers 390. The housing 387 includesmagnetic field generators, such as coils 391, mounted between polepieces 393. The housing 387 defines a cavity 395 connecting opposingopen ends 397, 399 of the housing 387. In this way, the piston 385 canpass through both open ends 397, 399 of the housing 387 during itsstroke. Accordingly, the axial length of the housing 387 can be muchshorter than the axial length of the piston 385, thereby providing acompact device. Trunnion mounts 401, which extend from the housing 387,allow the open ended housing 387 to be mounted to a separate device.

[0125] Turning to a partial view 39A, a bearing assembly 403 is locatedradially inward of each of the coils 391 and within radial grooves 404defined by the pole pieces 393 of the housing 387. Each bearing assembly403 includes an annular spring 405 (see also, FIG. 41B) located betweena coil 391 and an expandable bearing 407. Preferably, the spring is aband of compliant, elastomeric material, e.g., a sponge material or anO-ring.

[0126] The expandable bearing 407 contacts the surface of the piston 385and is biased by the spring 405 radially inward toward the outer surfaceof the piston 385. As a result, a small gap 409 is maintained betweenthe housing 387 and the piston 385 when the coils 391 are not energized.Preferably, the radial thickness of each bearing 407 is greater than thethickness of the gap 409 so that the bearing remains captured within therespective radial groove 404. Preferably, only the bearings 407 contactthe outer surface of the piston 385 when the magnetically actuatedmotion control device is in its off-state. By spacing a plurality ofbearings 407 axially along the housing 387, the piston 385 and thehousing 387 are prevented from binding, or moving out of axial alignmentrelative to one another (also referred to as “cocking”) when the deviceis in an off-state.

[0127] Energizing the coils 391 causes the fingers 390 to flex in aradially outward direction and press against the inner surface of thehousing 387. At the same time, each bearing 407 is pressed outward bythe fingers 390, thereby compressing the spring 405. Thus, when themotion control device 383 is in its on-state, the gap 409 between thehousing 387 and the piston 385 is eliminated as seen in FIGS. 40, 40Aand 41A as the magnetic field generated by the coils 391 causes thehousing 387 and the piston 385 to press firmly against one another.

[0128] In order to provide firm contact between the housing 387 and thepiston 385, the bearing 407 must expand radially as the fingers 390 flextoward the housing 387 in response to a magnetic field generated by thecoils 391. As seen in FIG. 41C, one embodiment of the annular bearingincludes a split 411 to allow for radial expansion. Optionally, split411 can be eliminated by forming bearing 407 of a material flexibleenough to permit its radial expansion. Preferably, the bearing is madefrom a strip of flexible, low friction material. Examples of suitablebearing materials include nylon materials, e.g., molybdenum disulfidefilled nylon fibers, Hydlar HF (A. C. Hyde Company, Grenloch, N.J.),which is a material including nylon reinforced with Kevlar fibers,polytetrafluorethylene materials, e.g., Teflon®, Derlin AF® (E. I.Dupont Nemours and Co., Wilmington, Del.), which is teflon filled withan acetal homopolymer, and Rulon® (Dixon Industries, Bristol, R.I.),which is a material including Teflon® reinforced Kevlar® fibers, Vespel®(E. I. Dupont Nemours and Co., Wilmington, Del.), which is a polyimidematerial, Ryton® (Philips Petroleum Co., Battlesville, Okla.), which isa material including polyphenylene sulfide filled with carbon fiber, orbrass. The preceding list is not exhaustive, and other suitablematerials will be apparent to one with ordinary skill in the art.

[0129] As explained earlier, the magnetic field generators, e.g., coilscan be mounted to either the housing or the piston with the other of thehousing or the piston being split into one or more flexible fingers.FIG. 42 shows a twenty-second embodiment of the present inventionincluding a piston 413 having two magnetic coils 391 located within acore 414 and a slotted housing 415 in which the piston 413 is located.Like the embodiments discussed in reference to FIGS. 1 and 2, thehousing 415 includes one or more longitudinal slots 417 that define oneor more flexible fingers 419.

[0130] The piston 413 slides within the housing 415 on bearingassemblies 421, which are each located radially inward of the coils 391and bear against the inner surface of the housing 415. Each bearingassembly includes an annular spring 425, which is located between anannular bearing 427 and one of the respective coils 391. The spring 425biases the bearing 427 radially outward and away from the magneticallyactive portion of the piston to create a gap 428 between the outersurface of the piston 413 and the inner surface of the housing 415.Preferably, each bearing 427 and spring 425 are of the same structuresand materials as those discussed in reference to FIGS. 39-41.

[0131] According to a twenty-third exemplary embodiment shown in FIG.43, bearing assemblies are located axially spaced from coils 391. Inthis embodiment a piston 429 is located within a housing 430 havingstructure such as that described in reference to FIG. 42, includingslots 432 defining one or more fingers 434. The piston 429 includes amain body 431 having a shoulder 433 at one end, an end cap 435 includinga shoulder 436 that opposes the shoulder 433 and two steel cores 437sandwiched between the end cap 435 and the main body 431.

[0132] A first bearing assembly 439 is located between the cores 437 andthe shoulder 433 in the cores 437. A second bearing assembly 441 islocated between the shoulder 436 and the main body 431. Each bearingincludes a spring 438 that biases a bearing 440 against the innersurface of the housing 430. Preferably, the spring 438 and bearing 440are constructed in the same manner as described with respect to theprevious embodiments. The bearings 440 are biased against the innersurface of the housing 430 to create a gap 442 between the cores 437 andthe inner surface of the housing 430 when the coils are not energized,i.e., the magnetically actuated motion control device is in anoff-state.

[0133] The cores 437 are secured to the main body of the piston 429 byan interference fit between the outer surface of the cores 437 and theinner surface of the piston 429. The cores 437 and end cap 435 aresecured to one another by a bolt 443 and a nut 445. The bolt 443 passesthrough aligned bores in the cores 437 and the end cap 435. Accordingly,as exemplified by this embodiment, the bearing assemblies need not belocated between the magnetic field generator (e.g., coils 391) and theopposing slotted member.

[0134] While two magnetic field generators, e.g., coils 391, areillustrated in FIGS. 39-42, one of ordinary skill in the art willreadily appreciate that one, or three or more, magnetic field generatorsmay alternatively be used within the spirit and scope of the invention.Similarly, although two bearing assemblies are illustrated in FIGS.39-42 one or more bearing assemblies may be used within the spirit andscope of the invention.

[0135] Advantages of using bearing assemblies in a magnetically actuatedmotion control device in order to create a gap between the housing andthe piston include maintaining the piston and the housing in axialalignment and creating smooth, fluid-like, relative movement between thehousing and the piston while the damper is in its off-state.

[0136] An example of a situation in which it may be important to providesmooth movement between the housing and the piston is when an embodimentof the present invention is used as a locking mechanism in a hingedvehicle door. In the example shown in FIG. 44, a car 447 includes a body449 and a door 451 that swings on a hinge 453 relative to the body 449.The housing 387 of a motion control device 383 (shown in FIGS. 40-41C)is mounted in the door 451 of the car 447. Because the door 451 haslimited space in which to fit extra components, the housing 387 ispreferably short relative to the length of the piston 385. The slottedpiston 385 is attached at one end to the body of the car. As the door isswung open and closed, the piston 385 moves within the housing 387. Anoperator can lock the door 451 into any position by activating a switch455 which energizes the magnetic field generator to cause the piston andthe housing to press against one another together, thus holding the doorin position.

[0137] The present invention has been described with reference toexemplary embodiments. However, it will be readily apparent to thoseskilled in the art that it is possible to embody the invention inspecific forms other than as described above without departing from thespirit of the invention. The exemplary embodiments are illustrative andshould not be considered restrictive in any way. The scope of theinvention is given by the appended claims, rather than the precedingdescription, and all variations and equivalents which fall within therange of the claims are intended to be embraced therein.

What is claimed is:
 1. A sensor for sensing a dynamic state of a movablemember in a magnetically actuated motion control device, themagnetically actuated motion control device including a housing defininga cavity in which the movable member is located, the sensor comprising:a first member secured to the housing of the magnetically actuatedmotion control device; and a second member coupled to the movablemember, wherein relative position between the first member and thesecond member indicates the position of the movable member relative tothe housing.
 2. A system comprising: A) a washing machine including ahousing and a drum, the drum being movable relative to the housing; andB) at least one magnetically actuated motion control device mountedbetween the drum and the housing, each at least one motion controldevice comprising a first member defining a cavity; a second memberpositionable within the cavity and being movable relative to the firstmember when positioned therein; at least one of the first and secondmembers including one movable finger; and a magnetic field generatorlocated on another of the first member and the second member, themagnetic field generator causing one of a portion of the first memberand a portion of the second member to press against the other of theportion of the first member and the portion of the second member.
 3. Asystem comprising: A) a chair including a seat and a base, the seatbeing movable relative to the base; and B) at least one magneticallyactuated motion control device mounted between the seat and the baseeach at least one motion control device comprising a first memberdefining a cavity; a second member positionable within the cavity andbeing movable relative to the first member when positioned therein; atleast one of the first and second members including one movable finger;and a magnetic field generator located on another of the first memberand the second member, the magnetic field generator causing one of aportion of the first member and a portion of the second member to pressagainst the other of the portion of the first member and the portion ofthe second member.
 4. A system comprising: A) a chair including a seat,at least one armrest and a base, the seat and at least one armrest beingmovable relative to the base; and B) at least one magnetically actuatedmotion control device mounted between the at least one armrest seat andthe base each at least one motion control device comprising a firstmember defining a cavity; a second member positionable within the cavityand being movable relative to the first member when positioned therein;at least one of the first and second members including one movablefinger; and a magnetic field generator located on another of the firstmember and the second member, the magnetic field generator causing oneof a portion of the first member and a portion of the second member topress against the other.
 5. A system comprising: A) a chair including aseat, at least one armrest, a backrest and a base, the seat and at leastone armrest being movable relative to the base; and B) at least onemagnetically actuated motion control device mounted between the backrestseat and each of the at least one armrest, each of the at least onemotion control device comprising a first member defining a cavity; asecond member positionable within the cavity and being movable relativeto the first member when positioned therein; at least one of the firstand second members including one movable finger; and a magnetic fieldgenerator located on another of the first member and the second member,the magnetic field generator causing one of a portion of the firstmember and a portion of the second member to press against the other. 6.A system, comprising: A) a table having a top and a plurality ofadjustable legs, each adjustable leg having a first portion and a secondportion, the first portion being movable relative to the second portion;and B) a magnetically actuated motion control device mounted between thefirst portion and the second portion of at least one of the adjustablelegs, the motion control device comprising a first member defining acavity; a second member positionable within the cavity and being movablerelative to the first member when positioned therein; at least one ofthe first and second members including one movable finger; and amagnetic field generator located on another of the first member and thesecond member, the magnetic field generator causing one of a portion ofthe first member and a portion of the second member to press against theother.
 7. A system comprising: A) a first surface and a second surface,the first surface moveable relative to the second surface; and B) amagnetically actuated motion control device mounted between the firstsurface and the second surface, the motion control device comprising afirst member defining a cavity; a second member positionable within thecavity and being movable relative to the first member when positionedtherein; at least one of the first and second members including onemovable finger; and a magnetic field generator located on another of thefirst member and the second member, the magnetic field generator causingone of a portion of the first member and a portion of the second memberto press against the other.
 8. A system comprising: A) a wheel connectedto a shaft; and B) a first magnetically actuated motion control devicecoupled to the shaft, the motion control device comprising a housingdefining a cavity; a stator having a center axis and being positionablewithin the cavity, the stator and housing being relatively rotatablerelative to the axis; the housing including one movable finger; and amagnetic field generator located on another of the housing and thestator, the magnetic field generator causing the finger to press againstthe stator.
 9. The system according to claim 8, further comprising: C) asecond magnetically actuated motion control device like said firstmotion control device, the second magnetically actuated motion controldevice being coupled to the shaft opposite the first magneticallyactuated motion control device; and D) a motor being coupled to thehousing of the first magnetically actuated motion control device and tothe housing of the second magnetically actuated motion control devicesuch that as the motor turns the housing of the first magneticallyactuated motion control device and the housing of the secondmagnetically actuated motion control device in opposite directions. 10.A system comprising: A) a housing including an opening; B) a balllocated within the housing so that a portion of the ball protrudesthrough the opening in the housing, the ball being rotatable relative tothe housing; C) a first shaft in rolling contact with the ball, thefirst shaft being coupled to a first magnetically actuated motioncontrol device comprising a housing defining a cavity; a stator having acenter axis and being positionable within the cavity, the stator andhousing being relatively rotatable relative to the axis; the housingincluding one movable finger; and a magnetic field generator located onanother of the housing and the stator, the magnetic field generatorcausing the finger to press against the stator; and D) a second shaftpositioned substantially perpendicular to the first shaft, the secondshaft being in rolling contact with the ball, the second shaft beingcoupled to a second magnetically actuated motion control device likesaid first magnetically actuated motion control device.
 11. A systemcomprising: A) a container for holding an irregularly shaped object; andB) a plurality of magnetically actuated motion control devices, eachmagnetically actuated motion control device having a first end andsecond end, the first end of each magnetically actuated motion controldevice having an extension cap, the second end of each magneticallyactuated motion control device being mounted to the container.
 12. Asystem comprising: A) a steering wheel; B) a steering column coupled tothe steering wheel and being movable relative to the steering wheel; andC) a magnetically actuated motion control device, the magneticallyactuated motion control device including a first end and a second end,the first end of the magnetically actuated motion control device beingmounted to the steering column and the second end being mounted to thesteering wheel, the magnetically actuated motion control devicecomprising: a first member defining a cavity; a second memberpositionable within the cavity and being movable relative to the firstmember when positioned therein; at least one of the first and secondmembers including one movable finger; and a magnetic field generatorlocated on another of the first member and the second member, themagnetic field generator causing one of a portion of the first memberand a portion of the second member to press against the other of theportion of the first member and the portion of the second member.